Primary cell with permanganate depolarizer



PRIMARY CELL WITH PERMANGANATE DEPOLARIZER Filed March 14, 1945 'Il' im!15 News VOL T5 0 5 1015 zo 2530 05 40 45 50550005 7o 1580 8s 0095100105110115120125 I JNVENTOR BY Samuel Euh/rv v v" jy" 1. l l

nTToNY 0 Patented Mar. 1, 1949 UNITED STATES PATENT OFFICE PRIMARY CELLWITH PERMANGAN ATE DEPOLARIZER Samuel Ruben, New Rochelle, N. Y.

Application March 14, 1945, Serial No. 582,594

(Cl. 13G-107) 20 Claims. 1

This invention relates to primary cells of the alkaline type. In itspreferred embodiment it relates to sealed dry type alkaline primarycells.

An object of the invention is to improve primary cells and theelectrodes thereof.

The present invention contemplates a primary cell embodying a cathodeformed of a depolarizer composition using silver or copper permanganateintimately mixed with a conductive material. The invention alsocontemplates features of cell construction which facilitate effectiveuse of the cathode and other cell materials. Other aspects of theinvention will be apparent from the following description taken inconjunction with the accompanying drawing, in which Figure 1 issectional View of a sealed alkaline dry cell embodying features of theinvention;

Figure 2 is a bottom view thereof;

Figure 3 is a section of a flat type cell;

Figures 4 and 5 are longitudinal and transverse sections of another cellconstruction; and

Figure 6 is a graph showing curves of primary cell voltage versus timeunder load.

The present invention contemplates a primary cell embodying a cathodeformed of a depolarizer composition using silver or copper permanganateintimately mixed with a conductive material. The invention alsocontemplates features of cell construction which facilitate effectiveuse of the cathode and other cell materials. Other aspects of theinvention will be apparent from the following description and claims.

Referring to the drawings Figures 1 and 2 show a primary cell comprisinga steel cup or container I in the bottom of which is pressed a cathodepellet l l of depolarizer composition.

In the preferred embodiment of the present invention the cathodedepolarizer composition l I is an intimate mixture of silverpermanganate and graphite so as to produce an electrically conductivecathode element. In order to obtain the best results the graphiteparticles should be finer than the permanganate particles and the twoshould be intimately mixed or ball milled together so that thepermanganate particles are substantially coated with a graphite film.The permanganate should be as pure as possible and nely divided.Micronized Ceylon graphite (for example, Dixons 200-09 and 200-12) showssuperior properties for this purpose. While the proportions of thegraphite may be Varied over a considerable range the most suitablecompositions contain 1 to 50% graphite and 20 to 30% graphite ispreferred, although the specific application of the cell may determinethe preferred graphite 2 amount. The composition is compacted to a densebody, a pressure of about 20,000 pounds per square inch being advisable.The ionic conductivity of the solid permanganate crystal is too low toallow its functioning as a cathode depolarizer without addition of aconductive agent.

While graphite is the preferred conductive material other nely dividedconductive materials may be substituted for it, or mixed with it, suchas very fine silver, silver oxide and the like.

A porous electrolyte-permeable barrier layer is disposed over the topsurface of depolarizer Il. The preferred barrier consists of one or moreporous discs I2 of a non-oxidizable material., preferably fibrouspolystyrene. These may be punched from a 5 mil sheet and then pressedinto the cup on top of the depolarizer. Other suitable organicnon-oxidizable materials, such as fibrous nylon sheet etc., may be used.Other barriers which are suitable are a pressed disc of magnesiumsilicate or magnesium hydroxide powder or a mixture of both, or ofceramic powder. These are pressed into the cup simultaneously withpressing of the depolarizer or as a subsequent operation. It is ofadvantage to use an inert inorganic barrier or non-oxidizable organicbarrier in contact with the permanganate-graphite electrode to avoidsurface reduction of the permanganate. Cellophane and dialysis parchmentpaper, while they can be used, are not quite so desirable for thisreason.

The anode assembly for the cell comprises a roll of corrugated zinc foilI4 interleaved with a double layer I5 of polystyrene bre sheet or, insome instances, porous paper. The zinc foil edge extends beyond the brelayer slightly at one end and the fibre layer extends beyond the zinc atthe other end of the roll. At least one complete turn of the fibre sheetencloses the outermost turn of the zinc at the outside of the roll. Animpervious insulating sleeve I6 of polystyrene or paper impregnated withpolystyrene or other alkali-resistant insulating material encloses theroll and holds it assembled and insulated from the walls of container. Asuitable method of making this anode assembly is shown and described inmy co-pending application Serial No. 513,687, filed December 10, 1943,now Patent No. 2,422,046.

The anode roll is impregnated with an alkaline electrolyte solution andthe zinc foil is amalgamated with mercury in the 'same operation. Anoderolls are placed in a flat bottom dish with the zinc end up and theelectrolyte is poured into the dish slowly allowing the electrolyte tobe drawn up into the rolls by capillarity. The porous fibre absorbs theelectrolyte and swells into the space afforded by the corrugations ofthe zinc. Electrolyte isr added to cover the rolls and then a measuredquantity of mercury is placed on top of each roll in contact with thezinc. A suitable proportion of lmercury is 5 to 20% of the weight of thezinc. The dish is then placed in an oven at 60 C. for several hours oruntil amalgamation of the zinc foil surface is substantially complete.

The rolls are then drained and moderate vacuum applied to removeentrapped gas bubbles. An impregnated anode in this condition is thenplaced in the container Il) with the projecting bre end incontact withthe less porous polystyrene discs I2 which absorb some of theelectrolyte froml the projecting fibre end.

An amalgamated zinc top disc Il of pie-pan shape is placed in the mouthof the container I with its depressed center in contact with theprojecting zinc foil I4 of the anode roll. A neoprene grommet ring I8encloses the edge of disc I1 and rests on a shoulder I9 formed in thecontainer wall. A at steel ring or washer 21;l is placed over thegrommet and the free edge 2| of the container is turned or spun downover the top of the washer to place the grommet under compression andseal the cell.

If desiredthe grommet can be sealed to the surface of the zinc disc withneoprene cement to further insure against electrolyte creepage. Aterminal tab 22 is soldered or spot welded to the center of the top discand then the entire exposed outer zinc surface is sprayed or paintedwith an air-excludinglacquer 23, such as a mixture of hydrogenated rosinplasticized with mineral oil.

Best performance is obtained from cells having the electrode `and spacerelements held together under substantial pressure by the containerparts. Thus, it is desirable that the anode roll assembly I4, I becompressed by the sealing operation as much as*10% or more. Y

The preferred electrolyte is a solution of potassium hydroxide which hasbeen substantially saturated with zincoxide by heating in the presenceof excess zinc oxide and then filtering. A solution containing about 38%KOH and 6.4% ZnO is very satisfactory although the concentration canfbevaried over a wide range. most practical applications the KOH amounts toabout to 50% of the solution with sufficient ZnO to saturate thesolution. This electrolyte andI its advantages are described more fullyin my co-pending application Serial No. 486,367, filed May 10, 1943, aswell as application Serial No. 513,687 above referred to.

Other electrolytes can be used in the cell, especially Where it isintended for use at low temperature and appropriate venting means areused, such as straight solutions of KOH, NaOH or LiOH or mixtures ofthese.

In some cases it may be necessary or desirable to provideventing means,which are normally closed but which will relieve gas pressure, shouldany*` gas develop after complete use of the depolarizer. One convenientventing arrangement is illustrated in Figures 1 and 2, which comprises apair of crossed chisel grooves 24 on the bottom of the container whichdo not completely penetrate the wall. The cell is therefore completelysealed but if gas pressure should develop the cross will open upsuiiciently to permit escape ofthe gas. Another method is to amalgamatethe zinc top to such an extent as to become brit- For.

tle so that if an excess gas pressure is had after complete use of thedepolarizer, any bulging caused by the gas pressure will cause cracks toappear and venting takes place through the cracks. Still another methodof venting is to use a porous oil impregnated sealing grommet ofneoprene or other .suitable inert resilient material in a ring shapesuch as shown at I8. This allows some passage of gas. outward throughthe porous grommet should internal gas pressure develop.

Figure 6 is a graph showing curves of voltage versus time under loadobtained with cells of the construction described having depolarizercathodes of AgMnO4 mixed with 20% micronized graphite, and of CuMnOimixed with 20% graphite. The cells had a diameter of '7/8 inch and were5/8 inch high. The zinc anodes were each formed of 2 mil zinc foilcorrugated with 2 mil deep corrugations the corrugated foil strips being792- inch wide and 36` inches long. The foil is wound up with two 4 milporous paper spacers inch wide. The depolarizer in each case was formedinto a pellet and compressed into the bottom of the can at 20,000 poundsper square inch.

The AgMnO4-graphite pellet weighed 2.9 grams.

The CuMnOi-graphite pellet weighed 2.1 grams. The paper spacers wereimpregnated with 2.5 grams of electrolyte containing 38% KOH and 6.4%dissolved ZnOz. The barrier I2 consisted of two 5 mil porous polystyrenefibre discs. The areas of the top of the cathode pellets were 0.54Ysquare inch.

The cells were each discharged through a 111 ohm load until theirvoltages fell to an arbitrary cut-01T value of 0.9 volt. It will benoted from graph curve 25, for the cell using silver permanganate thatthe initial voltage under load was 1.86 volts and after an initial dropthe curve attens out considerably reaching 0.9 volt after 125 hoursunder continuous load. Curve 26 is a similar curve for the CuMnO4 cell.The cut-off voltage was reached after -about 42 hours.

The two curves represent continuous initial runs under 111 ohm loaduntil the voltage dropped to 0.9 volt. If the cells are allowed torecuperate the voltage rises again and further output can be obtainedabove the cut-off voltage for several cycles, giving a much longer totalrun.

The original open circuit voltage of the silver permanganate cells was1.96 volts and that of the copper permanganate cells 1.94 volts.

Cells made without graphite or other conductive material mixed with thepermanganates dropped off in voltage to a low value almost as soon asthey were connected to a load.

Figure 3 shows a flat cell construction comprising a shallow Steel cup30 containing a silver or copper permanganate-graphite depolarizercathode 3l and a pressed zinc powder anode 32. The depolarizercomposition 3I is pressed in the bottom of the container 30 and abarrier disc 33, which may be porous polystyrene, pure asbestos, pressedglass powder, zinc oxide, magnesium silicate or magnesium hydroxidepowder for example, is pressed on top of it. An insulating sleeve ring35 is set on the barrier and against the side wall of the cell. This maybe of polystyrene or other alkali-resistant pliant material.

One or more porous fibre discs 34 are impregnated with electrolyte andlaid on the barrier inside the sleeve 35. The anode comprises a discpressed from iron-free zinc powder which has been amalgamated with 5 to15% of mercury. It may also be made from zinc granules or pellets whichhave been amalgamated. Amalgamated zinc top 36 presses against the topof the anode and holds it tightly against bre disc 34. The top 36 issealed in the mouth of cup by neoprene grommet 31 which is compressedagainst it by the enclosing edge of the container.

Figures 4 and 5 illustrate a cylindrical electrode construction in aprimary cell embodying other features of the present invention. The deepsteel container 4B has a liner disc 4| of polystyrene on its bottom.Upon this rest a group of concentric cylinders. The outer cylinder 42 isof pressed permanganate-graphite composition and is tted or pressedrather tightly against the cylindrical can wall.

The anode comprises a pressed amalgamated zinc powder cylinder 43 whichstands slightly higher than the depolarizer electrode. Between the anode43 and the depolarizer cathode 42 is a spacer 44 comprising a windingabout 40 mils thick of porous polystyrene bre sheet, or the combinationof paper adjacent the anode and polystyrene fibre adjacent the cathode.

Instead of layers of sheet materials, the spacer can be of a compressedabsorbent material such as a pressed cylinder of a mixture of magnesiumhydroxide and magnesium silicate, polystyrene fibres or a ceramicmaterial.

The hollow interior of the anode is filled with a wad or roll 46 ofporous polystyrene nbre or paper. The electrolyte is added to this rolland quickly passes through the porous anode and spacer 44 by capillaryaction and even to some extent into the depolarizer to eiect uniformdistribution of electrolyte. No excess free flowing electrolyte isallowed to remain. The bre or paper swells in the electrolyte exerting apressure against the anode and cathode cylinders. Polystyrene ring disc49 covers the top of cylinders 42 and 44.

The amalgamated zinc top 41 is pressed against the top end of anodecylinder 43 and is sealed in the mouth of the container by neoprenegrommet 48. It will be noted that the length of the cell can be variedwithout changing the ratio of the anode and cathode volumes or surfaces.

During cell operation the electrolyte reacts with the zinc and zinchydroxide is precipitated on the anode forming a coating thereon. Byusing an anode of large surface area as set forth in my above mentionedapplications the coating never reaches a thickness where it willinterfere with useful operation of the cell until the depolar'zer hasbeen consumed. ,For maximum cell life the zinc surface area should bepreferably at least 4 square inches per gram of the depolarizer.

' The electrolyte is constantly regenerated so that only a smallquantity is necessary to the continued functioning of the cell.

The cells described herein are found to have a longer life onintermittent service than on continuous use at the higher drains Theyappear to recuperate and return to higher voltage during periods ofnon-use.

It is of importance in avoiding local action fo the zinc used for theanode to be substantially pure. The iron content particularly should bekept low, preferably below .003%. Other metals such as copper and tinshould be kept below this proportion.

The barrier layer between the cathode and the anode being electrolytepermeable permits cell operation but substantially prevents migration ofcompounds from the cathode toward the anode.

The cell contains no free-flowing or freely-circulating electrolyte, asa result of keeping the weight ratio of electrolyte to bre between 3:1and 6:1 in the case where polystyrene bre is used. This factor furtherrestricts travel of compounds to the anode where they would causedeleterious local action and is one of the most basic factors necessaryfor long shelf life.

In relation to the depolarizer the amount of electrolyte within the cellmay be about 0.3 gram per gram of depolarizer in the flat andcylindrical structures and about 0.8 gram electrolyte per gram ofdepolarizer in the coiled foil anode type.

In the manufacture of the cell it is desirable that the permanganate andgraphite be substantially compressed as to produce an electricallyconductive mass. An excess of electrolyte is to be avoided.

There should be only sufficient electrolyte in the spacer to allowconduction and ionic migration but insuiiicient to allow dissolving ofthe permanganate by circulation or flow of the electrolyte. If thepermanganate is used with a wet or free flow electrolyte construction itwould rapidly dissolve and decompose into the electrolyte and adequateshelf life would not be possible.

The barrier is of considerable importance. It should limit circulationof the electrolyte and it should have substantially no reducing actionon the permanganate, particularly where high temperature ope-ration ofthe cell is to be encountered.

The use of the more reactive organic materials, such as paper, incontact with the depolarizer is generally to be avoided. The more stableorganic materials, such as polystyrene fibre, or inorganic barriers arepreferred. While paper can sometimes be used in other parts of the cell,such as for spacing apart the turns of the anode foil, some advantage isgained even here in using a less reactive material.

The permanganates described in this application as well as the onesdescribed in my prior application Serial No. 575,090 are the watersoluble permanganates. The combination and arrangement of cell elementsdescribed herein makes possible the use of such soluble permanganates insolid form. For example, the use of an electrolyte retaining spacer orbarrier layer in contact with the cathode prevents free circulation ofthe electrolyte which would dissolve and carry away the permanganate butpermits the ionic conduction necessary for cell operation, and permitseicient depolarizer action at the cathode surface.

While specic embodiments of the invention have been described, it isintended to cover the invention broadly within the spirit and scope oflthe appended claims.

What is claimed is:

1. A primary cell comprising a zinc anode, a cathode comprising anintimate mixture of a permanganate selected from the group consisting ofsilver and copper permanganates in solid state and a finely dividedconductive material. a porous spacer between said anode and cathode andin contact therewith, and an alkaline electrolyte absorbed in saidspacer.

2. A primary cell comprising a zinc anode, a cathode comprising anintimate mixture of a permanganate selected from the group consisting ofsilver and copper permanganates and a iinely divided conductivematerial` a porous spacer between said anode and cathode and in contacttherewith, and an alkaline electrolyte absorbed in said spacer, saidcell being characterized bythe absence of any freely flowing electrolytenot held in said spacer.

3. A primary cell comprising a zinc anode, a cathode comprising anintimate mixture of graphite and a permanganate of metal selected fromthe group consisting of silver and copper, a porous spacer between saidanode and cathode and in contact therewith, and an alkaline electrolyteabsorbed in said spacer, a container for said anode, cathode andelectrolyte impregnated spacer, and conductive terminals comprising partof said container, and connected respectively to said anode and cathode,and sealing means insulating said terminals from each other and sealingsaid cell.

4. A primary cell comprising a zinc anode, a cathode comprising solidpermanganate of a metal selected from the group consisting of silver andcopper, and a conductive material mixed therewith, a porous spacerbetween said anode and cathode and in contact therewith, at least partof said spacer comprising porous substantially inert organic fibre, andan alkaline electrolyte absorbed in said spacer, said electrolyte insaid libre being present in proportions between 3 and 5 times the weightof said fibre.

5. A primary cell comprising a zinc anode, a cathode comprising solidpermanganate in- ,timate'ly mixed with graphite, said permanganate beingselected from the group consisting of silver and copper permanganates, aporous spacer between said anode and cathode and in contact therewith,and an electrolyte comprising an a1- kaline solution impregnating saidspacer.

6. A primary cell comprising a zinc anode, a cathode comprising solidpermanganate` inti- Vmately mixed with graphite of a finer particle sizethan that of said permanganate, said permanganate being selected fromthe group consisting of silver and copper permanganates, a porous spacerbetween said anode and cathode and in contact therewith, and anelectrolyte comprising an alkaline solution impregnating said spacer,said electrolyte being substantially saturated with alkali metal zincateand said anode having a large surface area.

7. A primary cell comprising a Zinc anode, a cathode comprising solidpermanganate of metal selected from the group consisting of silver andcopper intimately mixed with graphite of a finer particle size than thatof said permanganate, a porous spacer between said anode and cathodervand in contact therewith, and an electrolyte comprising an alkalinesolution impregnating said spacer, said electrolyte being substantiallysaturated with alkali metal zincate and said anode having a largesurface area, a hermetically sealed container having terminals connectedto said anode and cathode respectively, enclosing said anode, cathodeand electrolyte impregnated spacer, and said cell being furthercharacterized by the absence of any freely iiowing electrolyte therein.

8. A primary cell comprising a zinc anode, a cathode comprising anintimate mixture of solid permanganate of metal selected from the groupconsisting of silver and copper and a conductive material, a porousspacer between said anode and cathode and in contact therewith, and anelectrolyte comprising an alkaline solution impregnating said spacer,said spacer including a porous barrier of ionically permeablenon-reactive material which is inert to said electrolyte and to saidpermanganate covering the electrolyteengaging surface of said cathode.

9. A-primary cell comprising a zinc anode, a cathode comprising anintimate mixture of permanganate of metal selected from the groupconsisting of silver and copper and a conductive material, a porousspacer between said anode and cathode and in contact therewith, and anelectrolyte comprising an alkaline solution impregnating said spacer,said Aspacer including a porous barrier of ionically permeable materialwhich is inert to said electrolyte and to said permanganate covering theelectrolyte-engaging surface of said cathode and a layer of porous paperbetween said barrier and said anode.

l0. A primary cell comprising a zinc anode of large surface area, acathode comprising an intimate mixture of permanganate of an elementselected from the group consisting of silver and copper, andfinely-divided graphite, a porous spacer interposed between said anodeand cathode and in contact therewith, said spacer comprising a barrierlayer of semi-permeable material inert to said electrolyte and to saidpermanganate covering the electrolyte-engaging surface 'of said cathodeand a layer of porous paper between said barrier layer and said anode,and an electrolyte impregnating said spacer comprising a solution ofpotassium hydroxide substantially saturated with dissolved zinc oxide.

11. A primary Ycell comprising a cylindrical cathode formed of anintimate mixture off a permanganate of an element selected from thegroup consisting of silver and copper, and a finely-divided conductivematerial, a cylindrical anode spaced within said cathode andsubstantially concentric therewith formed of a pressed cylinder ofamalgamated zinc powder, a porous spacer between said anode and cathode,said spacer and anode being impregnated with an alkaline electrolyte.

12. An electrode for alkaline primary cells comprising a solidpermanganate of an element selected from the group consisting of silverand copper.

13. A cathode depolarizer element for alkaline primary cells comprisinga solid permanganate of a metal selected from the group consisting ofsilver and copper.

14. An electrode for primary cells comprising a substantiallynon-electrically conductive solid silver permanganate mixed with aconductive material.

15. A primary cell containing a cathode comprising a solid silverpermanganate, an anode comprising zinc, and an alkaline electrolyte.

16. A cathode depolarizer element for alkaline dry cells comprising amixture of crystals of a permanganate of an element selected from thegroup consisting of silver and copper, and graphite compressed into anelectrically conductive body.

1'7. A primary cell comprising a zinc anode, an alkaline electrolyte,and a cathode comprising solid silver permanganate, a barrier in contactwith said permanganate and interposed between it and said anode, saidbarrier permitting ionic conduction therethrough, said barrier beingsubstantially unreactive with said permanganate.

18. In a primary cell, a silver permanganate cathode, an anode, anelectrolyte absorbent nonreactive spacer and an inert porous barriermember in contact with said permanganate and said non-.reactive spacer,land an electrolyte in said spacer.

19. A primary cell comprising an amalgamated zinc anode, a cathodecomprising a conductive material mixed with a permanganate of metalselected from the group consisting of silver and REFERENCES CITEDcopper, a body of alkaline electrolyte between said anode and cathode incontact therewith, l'ghf fligwlgtgererences are of record in the and alayer of porous material substantially p inert to said permanganatecovering the elec- 5 UNITED STATES PATENTS trolyte-engaging surface ofsaid cathode. Number Name Date 20. A primary cell comprising an anode, a'720 592 Kohn Feb 17 1903 cathode formed of a 'permanganate of a metal14862726 Buffor Mar' 11 1924 selected from the grop consisting of silverand copper, and an electrolyte in contact therewith 10 FOREIGN PATENTSwhich is capable of generating a current by reaction therewith. NumberCOUNTY Date SAMUEL RUBEN 163,744 Great Britain May 30, 1921 a 'Q L

